1. Field
The present disclosure relates to green phosphors, methods of preparing the green phosphors, and white light-emitting devices including the green phosphors. More particularly, the present disclosure relates to green phosphors with good thermal stability, methods of preparing the green phosphors, and white light-emitting devices including the green phosphors.
2. Description of the Related Art
Fluorescent lamps and incandescent bulbs are widely used in typical lighting systems. However, mercury (Hg), used in fluorescent lamps, may cause environmental problems when improperly disposed of. Further, typical lighting systems, and particularly incandescent lighting systems, have very short lifetimes (typically less than about 1,000 hours of constant use) and low efficiencies (less than 200 lumens per watt). Thus, their use is undesirable or impractical for applications where reduced power consumption is desired. Correspondingly, much research has been performed to improve such characteristics as lifetime and efficiency, and as a result, the efficiency of white light-emitting devices has been improved.
In white light-emitting devices, white light is generated in various ways, such as for example, by exciting phosphors emitting in each of the three primary colors (red, green, and blue) of emitted light by using a ultraviolet light-emitting diode (“UV LED”) as a light source, by exciting red and green phosphors with a blue light emitting diode (“LED”) as a light source, and by exciting a yellow phosphor with a blue LED as a light source.
Phosphors used in white light-emitting devices need to efficiently absorb light emitted from an LED used to excite the phosphors, to emit light at high efficiency at a wavelength appropriate for its purpose, and to retain its initial luminance efficiency and light characteristics even at high temperatures. For example, a widely used green phosphor, (Ba,Sr)2SiO4:Eu2+, has high efficiency at room temperature. However, this green phosphor has very low thermal stability and thus, when driving a light-emitting device including this green phosphor at an increased temperature for the light-emitting device, the room-temperature efficiency of the green phosphor decreases rapidly.
The recently developed beta silicon-aluminum oxynitride (β-SiAlON) phosphors, have high efficiency and good thermal stability. However, since the β-SiAlON phosphor is synthesized at a high temperature of about 2,000° C. and at a high pressure of 10 atmospheres (atm; 1.01 megapascals, MPa) by using specialized and expensive production equipment, it is inefficient and difficult to produce the β-SiAlON phosphor in a large scale. Further, while SrSi2O2N2:Eu2+ phosphor has high efficiency and good thermal stability, the SrSi2O2N2:Eu2+ phosphor has an emission peak at a wavelength greater than 540 nm. Thus, the widely available green phosphors such as SrSi2O2N2:Eu2+ phosphor may not be appropriate for illumination with good color rendering properties, or as a phosphor with high color reproducibility.